Graphene-based laminate and method of preparing the same

ABSTRACT

Provided are a graphene-based laminate and a method of preparing the graphene-based laminate. The graphene-based laminate may include a substrate; a graphene layer formed on at least one surface of the substrate; and an inorganic layer formed on the graphene layer and including a fluorine-containing lithium compound.

CROSS-REFERENCE TO THE RELATED APPLICATION

This application claims priority from Korean Patent Application No.10-2016-0011873 filed on Jan. 29, 2016 in the Korean IntellectualProperty Office the disclosure of which is incorporated herein in itsentirety by reference.

BACKGROUND

1. Field

Apparatuses and methods consistent with exemplary embodiments of theinventive concept relate to a graphene-based laminate and a method ofpreparing the graphene-based laminate.

2. Description of the Related Art

Graphene has a two-dimensional structure having a hexagonal shape, inwhich a distance between two adjacent carbon atoms is about 1.42 Å.Graphene has excellent characteristics in terms of strength, thermalconductivity, and electron mobility, and thus, may be used in atransmissive electrode or various graphene-based electronic devices.

Accordingly, sheet resistivity or electric characteristics of graphenefor electrode application have been controlled by using an interlayermaterial. Also, a charge-carrier density of graphene has been controlledby introducing a conductive material, a self-assembled monolayer, orchemical or optical materials on graphene, or by performing a simpleultraviolet (UV) radiation or an acid-base treatment process ongraphene.

However, while these techniques may easily change the charge-carrierdensity, doping stability may be degraded.

Therefore, a graphene laminate having a novel structure, which is stablein terms of electron doping and has improved electron mobility, and amethod of preparing such graphene laminate are needed.

SUMMARY

Exemplary embodiments of the inventive concept provide a graphene-basedlaminate with improved electron doping stability and electron mobility.The exemplary embodiments provide a method of preparing thegraphene-based laminate which may be economical and may improve electronmobility.

Various aspects of the exemplary embodiments will be set forth in partin the description which follows and, in part, will be apparent from thedescription, or may be learned by practice of the presented embodiments.

According to an aspect of an exemplary embodiment, there is provided agraphene-based laminate which may include: a substrate; a graphene layerformed on at least one surface of the substrate; and an inorganic layerformed on the graphene layer and including a fluorine-containing lithiumcompound.

According to another aspect of an exemplary embodiment, there isprovided a method of preparing a graphene-based laminate which mayinclude: transferring a graphene layer onto a target substrate todispose the graphene layer on at least one surface of the targetsubstrate; and depositing an inorganic layer including afluorine-containing lithium compound on the disposed graphene layer.

According to still another aspect of an exemplary embodiment, there isprovided an organic light emitting device which may include: a firstelectrode including the above graphene-based laminate; a hole injectionlayer formed above the first electrode; a hole transport layer formedabove the hole injection layer; an emission layer formed above the holetransport layer; an electron transport layer formed above the emissionlayer; an electron injection layer formed above the electron transportlayer; and a second electrode.

According to yet another aspect of an exemplary embodiment, there isprovided a transistor which may include: a gate layer; a substrate andan insulating layer formed above the gate layer; a source electrode anda drain electrode formed above the insulating layer; and the abovegraphene-based laminate contacting the source electrode and the drainelectrode and disposed therebetween.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects will become apparent and more readilyappreciated from the following description of the exemplary embodiments,taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic view of a graphene-based laminate according to anexemplary embodiment;

FIG. 2 is a schematic view of a thermal chemical vapor deposition (CVD)device according to an exemplary embodiment;

FIG. 3 is a schematic view of an organic light-emitting device accordingto an exemplary embodiment;

FIG. 4 is a schematic view of a back-gated field-effect transistor (FET)according to an exemplary embodiment;

FIG. 5 is a graph of light transmittance measurement on graphenesubstrate laminates prepared in Reference Example 1 and ReferenceComparative Example 1;

FIG. 6 shows a Raman spectrum of graphene substrate laminate channellayers of the back-gated FETs prepared in Example 5 and ComparativeExample 2;

FIG. 7A is a graph showing I_(DS)−V_(GS) obtained when a drain sourcevoltage (V_(DS)=0.3V) is applied to the back-gated FETs prepared inExamples 4 and 5 and Comparative Example 2;

FIG. 7B is a graph showing a field effect mobility (μ_(FE)) of electronsand holes of the back-gated FETs prepared in Examples 4 and 5 andComparative Example 2;

FIG. 7C is a graph showing I_(DS)−V_(GS) obtained when a drain sourcevoltage (V_(DS)=0.3V) is applied to the back-gated FET prepared inExample 5 and the back-gated FET of Example 5 after 1 year;

FIG. 8A is a graph showing V_(NP) of a hole charge with respect to athickness of a LiF layer formed on a graphene layer of a graphene-basedlaminate in the back-gated FETs prepared in each of Examples 4 to 6 andComparative Example 2; and

FIG. 8B is a graph showing a field effect mobility (μ_(FE)) of a holecharge with respect to a thickness of a LiF layer formed on a graphenelayer of a graphene-based laminate in the back-gated FETs prepared ineach of Examples 4 to 6 and Comparative Example 2.

DETAILED DESCRIPTION

Reference will now be made in detail to exemplary embodiments of agraphene-based laminate and a method of preparing the graphene-basedlaminate examples of which are illustrated in the accompanying drawings,wherein like reference numerals refer to like elements throughout. Inthis regard, these embodiments may have different forms and should notbe construed as being limited to the descriptions set forth herein.Accordingly, the embodiments are merely described below, by referring tothe figures, to explain some aspects of the inventive concept. As usedherein, the term “and/or” includes any and all combinations of one ormore of the associated listed items. Expressions such as “at least oneof,” when preceding a list of elements, modify the entire list ofelements and do not modify the individual elements of the list.

As used herein, when a portion “includes” an element, another elementmay be further included, rather than excluding the existence of theother element, unless otherwise described.

As used herein, the term “on” refers to directly on the other element orintervening elements may also be present

As used herein, the term “graphene” refers to one polycyclic aromaticcarbon compound or a plurality of the polycyclic aromatic carboncompounds having a plurality carbon atoms linked by a covalent bond(generally, an sp² bond) arranged in a planar shape, and the carbonatoms linked by a covalent bond may form a 6-membered ring as a basicrepeating unit or may further include 3-membered ring, 4-membered ring,5-membered ring, and/or 6 or more-membered ring.

As used herein, the term “graphene” includes all of monocrystalline,polycrystalline, and non-crystalline graphene, and refers to “pristinegraphene” that does not have a functional groups attached on a surfacethereof.

As used herein, the term “doping” refers to a process of preparingcarriers by providing electrons to or removing electrons from a part ofa conjugated bonding π-orbit to provide conductivity to a conjugatedcompound, e.g., a polycyclic aromatic carbon compound. In other words,when new electrons are added to or removed from a conjugated compoundhaving a double bond, inside of hole molecules may be unbalanced, andthus, an electron orbit opens which allows migration of electrons. Here,the process of adding new electrons or removing electrons is referred toas “doping”.

When a semiconductor device is manufactured, a graphene-based laminatehaving a transition metal oxide such as Al₂O₃ or HfO₂ deposited ongraphene by atomic layer deposition (ALD) has been used.

However, the ALD process has an adhesion problem due to thehydrophobicity of graphene basal planes. Thus, prior to the ALD process,a nucleation site process, a metal vaporization process, and a postoxidation process need to be performed. However, despite these elaboratepreparation processes, unexpected deterioration of charge mobility hasbeen reported due to inherent impurity such as oxygen vacancy and softoptical phonons related to a large ion polarizibility of a high-ktransition metal oxide.

In order to address the problem, an exemplary embodiment of theinventive concept provides a graphene-based laminate which includes asubstrate, a graphene layer formed on at least one surface of thesubstrate, and an inorganic layer formed on the graphene layer. Here,the inorganic layer may include an inorganic material such as afluorine-containing lithium compound.

According to an exemplary embodiment, the inorganic material included inthe inorganic layer may be represented by Formula 1:Li_(x)F_(y)  (1)

In Formula 1, x may satisfy 1≤x≤10, and y may satisfy 1≤y≤10.

According to an exemplary embodiment, the inorganic material may includeat least one compound selected from LiF, LiF₂, LiF₃, Li₂F, and Li₃F₃.For example, the inorganic material may be LiF.

LiF is a polar dielectric having a high dielectric constant of about 9and a large band gap of about 13.6 eV, and thus, a material includingLiF is transparent. Due to such characteristics of a polar dielectricstructure, electron affinity may be induced, and thus, a work functionon a graphene layer may decrease during electron doping that forms theinorganic layer including a fluorine-containing lithium compound, i.e.,a layer including the inorganic material represented by Formula 1, onthe graphene layer.

Thus, in the graphene-based laminate according to the present exemplaryembodiment, self-passivation effect may be caused by the inorganic layerincluding a fluorine-containing lithium compound, i.e., a layerincluding the inorganic material represented by Formula 1. Further,since a Fermi level may be controlled, stable electron doping may occur.Also, screening impurities having charges increases by the inorganiclayer including a fluorine-containing lithium compound, and thus, acharge mobility may improve in the graphene-based laminate.

The inorganic layer may be in a form of a thin film.

FIG. 1 is a schematic view of a graphene-based laminate 1, according toan exemplary embodiment.

As shown in FIG. 1, the graphene-based laminate 1 includes a graphenelayer 3 formed on a substrate 2, and an inorganic layer 4 of afluorine-containing lithium compound, e.g., a LiF layer, is formed onthe graphene layer 3 in the form of a thin film. The inorganic layer 4of a fluorine-containing lithium compound, e.g., a LiF layer, may beeasily deposited on the graphene layer 3 by thermal chemical vapordeposition (CVD) at room temperature.

A thickness of the inorganic layer 4 of a fluorine-containing lithiumcompound, e.g., a LiF layer, may be irregular as a surface of thegraphene layer 3 is uneven or bumpy.

An average thickness of the inorganic layer may be in a range of about0.1 nm to about 10 nm. For example, an average thickness of theinorganic layer may be in a range of about 0.1 nm to about 5 nm.

As used herein, the term “average thickness” refers to a value ofaverage taken after adding distances from a surface of the graphenelayer 3, that is, where the graphene layer 3 is in contact with asurface of the inorganic layer 4, to an opposite surface of theinorganic layer 4. The average thickness may be obtained by measuringthe distances with, for example, a field ion microscope, or may beobtained by measuring the distances through depth profiling using anx-ray photoelectron spectroscopy (XPS), but embodiments are not limitedthereto, and any method available in the art for measuring an averagethickness may be used.

When the average thickness of the inorganic layer is within the rangesabove, stable electron doping effect with respect to the graphene layermay be sufficiently obtained while sufficiently maintainingcharacteristics of the graphene layer, and electron mobility improvingeffect may be sufficiently obtained.

The graphene layer may include one layer to ten layers. For example, thegraphene layer may be a monolayer. The graphene layer is economicalsince sufficient electron doping effect and sufficient electron mobilityimproving effect may be obtained even when the graphene layer is amonolayer.

The graphene layer may include graphene having defects on a surfacethereof. As used herein, the term “defects” refer to defects caused byphysical damages, and, for example, the defects may include pointdefects, cracks, folds, or wrinkles.

When an inorganic layer including a fluorine-containing lithiumcompound, e.g., an inorganic layer represented by Formula 1, is formedon the graphene layer having defects thereon, about 95% of the entiresurface area of the graphene layer has no defect, and thus thegraphene-based laminate may obtain stable electron doping effect andsufficient electron mobility improving effect.

The substrate may include at least one material selected from apolymer-based material, a silica-based material, and a metal oxide-basedmaterial. Examples of the polymer-based material may includepolyethylene terephthalate (PET), polyimide (PI), or polyacrylonitrile(PAN). Examples of the silica-based material may include SiO₂, glass, orquartz. Example of the metal oxide-based material may include Al₂O₃,sapphire, TiO₂, ZnO, ZrO₂, HfO₂, MgO, NiO, Co₂O, CuO, or FeO. Forexample, a thickness of the substrate may be in a range of about 10 nmto about 100 μm, but embodiments are not limited thereto.

The substrate may be a transfer substrate. The graphene layer on thetransfer substrate may include graphene having defects on a surfacethereof.

The graphene-based laminate may further include an additive layerbetween the graphene layer and the inorganic layer including afluorine-containing lithium compound, e.g., the inorganic layerrepresented by Formula 1. According to an exemplary embodiment, theadditive layer may include an additive, and examples of the additive mayinclude a polymer curing resin, a thermoplastic resin, or a foamingagent. The additive layer may increase charge mobility of the graphenelayer as well as adhesion strength with the graphene layer and maydecrease a sheet resistance.

According to another exemplary embodiment, a method of preparing agraphene-based laminate includes transferring a graphene layer onto atarget substrate to dispose the graphene layer on at least one surfaceof the target substrate; and depositing an inorganic layer including afluorine-containing lithium compound on the graphene layer.

The inorganic layer may be represented by Formula 1.

The graphene layer may be grown on a substrate, on which graphene andgraphitized catalyst layer are formed. An example of the substrate maybe a copper foil.

The graphene and graphitized catalyst layer may include at least onecatalyst selected from Cu, Ni, and an alloy thereof. The graphene andgraphitized catalyst layer may grow graphene of a monolayer bycontrolling temperature and gas regardless of a type of the substrate.For example, the graphene and graphitized catalyst layer may growgraphene of a monolayer at a high temperature of about 1000° C. orhigher.

The graphene layer may include one layer to 10 layers. For example, thegraphene layer may be a monolayer. The graphene layer is economicalsince sufficient electron doping effect and sufficient electron mobilityimproving effect may be obtained even when the graphene layer is amonolayer.

The transferring of the graphene layer to the target substrate mayfurther include etching the target substrate.

The transferring may be performed by, for example, forming apolymethylmethacrylate (PMMA) layer on a graphene layer/substratelaminate by using a common coating technique such as spin-coating. Thesubstrate may be immersed and etched in an acidic solution, e.g., 0.1 Mammonium persulfate (((NH₄)₂S₂O₈). The PMMA layer/graphene layerlaminate may be washed with water, and the resultant may be transferredto the target substrate. Acetone and vacuum annealing may be performedon the PMMA layer.

Alternatively, the transferring may be performed by, for example,attaching adhesive film on the graphene layer/substrate laminate. Theadhesive film may be, for example, an acrylate-based adhesive film. Thesubstrate may be immersed in an acidic solution, for example, apredetermined amount of a solution including sulfuric acid and hydrogenperoxide (H₂SO₄, H₂O₂) to perform etching. Then, the adhesivefilm/graphene layer laminate may be washed with a predetermined amountof water, attached on the target substrate, and heated to a temperaturein a range of about 100° C. to about 200° C. Thereafter, the adhesivefilm is removed from the substrate, and thus, graphene is transferred tothe target substrate.

The target substrate may include at least one material selected from apolymer-based material, a silica-based material, and a metal oxide-basedmaterial. The polymer-based material, the silica-based material, and themetal oxide-based material are the same as defined herein.

An average thickness of the inorganic layer may be in a range of about0.1 nm to about 10 nm. For example, an average thickness of theinorganic layer may be in a range of about 0.1 nm to about 5 nm.Definition and measuring method of the average thickness are the same asdescribed herein.

When the average thickness of the inorganic layer is within theseranges, stable electron doping effect with respect to the graphene layermay be obtained while sufficiently maintaining characteristics of thegraphene layer, and charge mobility improving effect may also beobtained.

The depositing of the inorganic layer may be performed by thermalchemical vapor deposition (CVD).

FIG. 2 is a schematic view of a thermal CVD device 11 according to anexemplary embodiment.

As shown in FIG. 2, the thermal CVD device 11 is equipped with a powersource 16, an outlet 15, which is an external pathway, and a vacuumchamber 13. The vacuum chamber 13 includes a substrate 12 and a heatresistance wire (W) 14 therein. A metal vapor 17 is generated betweenthe heat resistance wire (W) 14 and the substrate 12.

In order to deposit the inorganic layer including a fluorine-containinglithium compound, e.g., the inorganic layer represented by Formula 1, onthe graphene layer, a graphitized catalyst is removed from the growngraphene layer, transferred to a substrate such as SiO₂, and aphotolithography process is performed to prepare a graphene sample.Then, a source holder (a boat) holding the heat resistance wire (W) 14is heated at a high vacuum in a range of about 10⁻⁵ torr to about 10⁻⁷torr to melt and evaporate the inorganic material including afluorine-containing lithium compound, e.g., the inorganic materialrepresented by Formula 1, on the source holder (a boat). Here, theinorganic material represented by Formula 1 condenses on a surface ofthe graphene sample having a low temperature and thus may be deposited.

When the depositing of the inorganic layer is performed by thermal CVD,problems related to damages on the graphene layer by plasma generated ina sputtering process, heating cost for increasing a temperature of thesample during the CVD process or ALD process, and an adhesion strengthbetween the deposition material and the graphene layer may be resolved.

According to another exemplary embodiment, an electrode may include angraphene-based laminate.

FIG. 3 is a schematic view of an organic light-emitting device 20according to an exemplary embodiment.

As shown in FIG. 3, the organic light-emitting device 20 includes asubstrate (not shown), a first electrode 21, a hole injection layer 22,a hole transport layer 23, an emission layer 24, an electron transportlayer 25, an electron injection layer 26, and a second electrode 27.

The first electrode 21 may be an anode or a cathode. For example, thefirst electrode 21 may be an anode. Here, a substrate (not shown) of theorganic light-emitting device may be a substrate generally used in anorganic light-emitting device, and the substrate may be a glasssubstrate or transparent plastic substrate, each with excellentmechanical strength, thermal stability, transparency, surfacesmoothness, ease of handling, and water resistance. A material for thefirst electrode 21 may be indium tin oxide (ITO), indium zinc oxide(IZO), tin oxide (SnO₂), zinc oxide (ZnO), Al, Ag, or Mg having a goodconductivity, and the first electrode 21 may be a transmissive electrodeor a reflective electrode.

The first electrode 21 may be a transmissive electrode including agraphene-based laminate. The electrode may have a light transmittancethat is lower than that of a transmissive electrode including onlygraphene.

Next, the hole injection layer 22 may be formed on the first electrode21 by using various methods, such as vacuum-deposition, spin coating,casting, or Langmuir-Blodgett (LB) method.

When the hole injection layer 22 is formed by vacuum deposition, thedeposition may be performed, e.g., at a deposition temperature of about100° C. to about 500° C., a vacuum degree of about 10⁻⁸ torr to about10⁻³ torr, and a deposition rate of about 0.01 □/sec to about 100 □/secconsidering a compound for forming the hole injection layer 22 to bedeposited and a desired structure and thermal characteristics of thehole injection layer 22 to be formed.

When the hole injection layer 22 is formed by spin coating, the coatingmay be performed, e.g., at a coating speed of about 2,000 rpm to about5,000 rpm and at a temperature of about 80° C. to about 200° C. forremoving a solvent after the coating considering a compound for formingthe hole injection layer 22 to be deposited and a desired structure andthermal characteristics of the hole injection layer 22 to be formed.

Examples of a material for the hole injection layer 22 may include aphthalocyanine compound such as copper phthalocyanines, 4,4′,4″-tris(3-methylphenylphenylamino)triphenylamine (m-MTDATA),N,N′-di(1-naphthyl)-N,N′-diphenylbenzidine (NPB), TDATA, 2T-NATA,polyaniline/dodecylbenzenesulfonic acid (PANI/DBSA),poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT/PSS),polyaniline/camphor sulfonic acid (PANI/CSA), orpolyaniline/poly(4-styrenesulfonate) (PANI/PSS), but embodiments are notlimited thereto.

A thickness of the hole injection layer 22 may be in a range of about100 □ to about 10000 □, for example, about 100 □ to about 1000 □. Whenthe thickness of the hole injection layer 22 is within these ranges,excellent hole injection characteristics may be obtained without asubstantial increase in driving voltage.

Next, the hole transport layer 23 may be formed on the hole injectionlayer 22 by using various methods such as vacuum deposition, spincoating, casting, or the Langmuir-Blodgett (LB) method. When the holetransport layer 23 is formed by vacuum-deposition or spin coating,deposition and coating conditions for the hole transport layer 23 may bedetermined by referring to the deposition and coating conditions for thehole injection layer 22.

Examples of a material for the hole transport layer 23 may include acarbazole derivative such as N-phenyl carbazole or polyvinyl carbazole,NPB, or an amine derivative having an aromatic condensed ring such asN,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1-biphenyl]-4,4′-diamine(TPD).

A thickness of the hole transport layer 23 may be in a range of about 50□ to about 1000 □, for example, about 100 □ to about 600 □. When thethickness of the hole transport layer 23 is within these ranges,excellent hole transport characteristics may be obtained without asubstantial increase in driving voltage.

Next, the emission layer 24 may be formed on the hole transport layer 23by using various methods such as vacuum deposition, spin coating,casting, or the LB method. When the emission layer 24 is formed byvacuum-deposition or spin coating, deposition and coating conditions forthe emission layer 24 may be determined by referring to the depositionand coating conditions for the hole injection layer 22 although thedeposition conditions may vary depending on a compound that is used toform the emission layer 24.

According to an exemplary embodiment, the emission layer 24 may includea host and a dopant. Examples of the dopant may include a fluorescentdopant or a phosphorescent dopant.

Examples of the host may include Alq3, 4,4′-N,N′-dicarboxyliccarbazole-biphenyl (CBP), poly(n-vinylcarbazole) (PVK),9,10-di(naphthalene-2-yl)anthracene (ADN),1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene (TPBI),3-tert-butyl-9,10-di(naphth-2-yl)anthracene (TBADN), E3, ordistyrylarylene (DSA), but embodiments are not limited thereto.

The dopant may be a red dopant, and examples of the red dopant mayinclude PtOEP, Ir(piq)₃, Btp₂Ir(acac), or DCJTB, but embodiments are notlimited thereto.

Also, the dopant may be a green dopant, and examples of the green dopantmay include Ir(ppy)₃ (where ppy=phenylpyrridine), Ir(ppy)₂(acac),Ir(mpyp)₃, or C545T, but embodiments are not limited thereto.

Also, the dopant may be a blue dopant, and examples of the blue dopantmay include F2Irpic, (F2ppy)2Ir(tmd), Ir(dfppz)3, ter-fluorene,4,4′-bis(4-diphenylaminostyryl)biphenyl (DPAVBi), or2,5,8,11-tetra-t-butylperylene (TBP), but embodiments are not limitedthereto.

An amount of the dopant may be in a range of about 0.1 part to about 20parts by weight, or, for example, about 0.5 parts to about 12 parts byweight, based on 100 parts by weight of the material for the emissionlayer 24 (that is, the total weight of the host and the dopant is 100parts by weight). When the amount of the dopant is within these ranges,concentration extinction may be practically prevented.

A thickness of the emission layer 24 may be in a range of about 100 Å toabout 1000 Å, for example, about 200 Å to about 600 Å. When thethickness of the emission layer 24 is within these ranges, excellentemission characteristics may be obtained without a substantial increasein driving voltage.

When the emission layer 24 includes a phosphorescent dopant, a holeblocking layer (HBL) (not shown) may be formed on the emission layer 24in order to prevent diffusion of triplet excitons or holes to theelectron transport layer 25. Here, a material for the hole blockinglayer is not particularly limited, and any material available in the artas a hole blocking material may be used. Examples of the hole blockingmaterial may include an oxadiazol derivative, a triazol derivative, aphenanthroline derivative, Balq, or BCP.

A thickness of the hole blocking layer may be in a range of about 50 Åto about 1000 Å, for example, about 100 Å to about 300 Å. When thethickness of the hole blocking layer is within these ranges, diffusionof triplet excitons or holes to the electron transport layer 25 may beblocked without a substantial increase in driving voltage.

Next, the electron transport layer 25 may be formed by using variousmethods such as vacuum deposition, spin coating, or casting. When theelectron transport layer 25 is formed by vacuum-deposition or spincoating, deposition and coating conditions for the electron transportlayer 25 may be determined by referring to the deposition and coatingconditions for the hole injection layer 22 although the depositionconditions may vary depending on a compound that is used to form theelectron transport layer 25.

Examples of a material for the electron transport layer 25 may include aquinoline derivative, tris(8-hydroxyquinoline) aluminum(III) (Alq₃),TAZ, or Balq, but embodiments are not limited thereto.

A thickness of the electron transport layer 25 may be in a range ofabout 100 Å to about 1000 Å, for example, about 100 Å to about 500 Å.When the thickness of the electron transport layer 25 is within theseranges, excellent electron transport characteristics may be obtainedwithout a substantial increase in driving voltage.

Also, the electron injection layer 26 having a function to facilitateinjection of electrons from an anode may be deposited on the electrontransport layer 25.

Examples of a material for the electron injection layer 26 may includeLiF, NaCl, CsF, Li₂O, or BaO, which are generally used as a material forforming an electron injection layer in the art. Deposition and coatingconditions for the electron injection layer 26 may be determined byreferring to the deposition and coating conditions for the holeinjection layer 22 although the deposition conditions and coatingconditions may vary depending on a compound that is used to form theelectron injection layer 26.

A thickness of the electron injection layer 26 may be in a range ofabout 1 Å to about 100 Å, for example, about 5 Å to about 90 Å. When thethickness of the electron injection layer 26 is within these ranges,excellent electron injection characteristics may be obtained without asubstantial increase in driving voltage.

Then, the second electrode 27 may be formed on the electron injectionlayer 26 by vacuum deposition or sputtering. The second electrode 27 maybe used as a cathode or an anode. A material for forming the secondelectrode 27 may be a material having a low work function, and such amaterial may be metal, alloy, an electrically conductive compound, or amixture thereof. Examples the material for the second electrode 27 mayinclude lithium (Li), magnesium (Mg), aluminum (Al), aluminum-lithium(Al—Li), calcium (Ca), magnesium-indium (Mg—In), or magnesium-silver(Mg—Ag). According to an exemplary embodiment, a transmissive cathodeformed by using ITO or IZO may be used to obtain a top-emission device.

The organic light-emitting device 20 may be included in a variety typeof flat panel display apparatuses, for example, a passive matrix organiclight-emitting display apparatus and an active matrix organiclight-emitting display apparatus. Particularly, when the organiclight-emitting device 20 is included in an active matrix organiclight-emitting display apparatus, a first electrode 21 disposed on asubstrate is a pixel electrode, and the first electrode 21 may beelectrically connected to a source electrode or drain electrode of athin film transistor. In addition, the organic light-emitting device 20may be included in a flat panel display apparatus that may displayimages on both sides.

Also, when an organic layer of the organic light-emitting device 20includes a plurality of organic layers, at least one layer of theorganic layer may be formed by deposition, or by using a wet processingof a coating process using a compound in the form of a solution.

According to another exemplary embodiment, an electronic device mayinclude the graphene-based laminate. The electronic device may be, forexample, a field effective transistor, but a shape or a type of theelectronic device is not limited thereto, and any electronic deviceaccording to the need may be used. The field effective transistor (FET)may be, for example, a back-gated FET.

FIG. 4 is a schematic view of a back-gated field-effect transistor (FET)30 according to an exemplary embodiment.

As shown in FIG. 4, the back-gated FET 30 includes an Si-doped substrate32 and an insulating layer 33 sequentially stacked as a back gate on aback gate contact surface 31. A graphene-based laminate channel layer 34is in contact with a source electrode 35 and a drain electrode 36.

Here, a distance between the source electrode 35 and the drain electrode36 may be determined by a use of the back-gated FET 30. For example, adistance between the source electrode 35 and the drain electrode 36 maybe in a range of about 0.1 μm to about 1 mm, or, for example, about 1 μmto about 100 μm, or about 5 μm to about 100 μm.

Materials for the source electrode 35 and the drain electrode 36 are notparticularly limited as long as they are conductive, and examples of thematerials may include platinum, gold, silver, nickel, chrome, copper,iron, tin, antimony, lead, tantalum, indium, palladium, tellurium,rhenium, iridium, aluminum, ruthenium, germanium, molybdenum, tungsten,tin antimony oxide, indium tin oxide (ITO), fluorine-doped zinc oxide,zinc, carbon, graphite, glassy carbon, silver paste and carbon paste,lithium, beryllium, sodium, magnesium, potassium, calcium, scandium,titanium, manganese, zirconium, gallium, niobium, sodium-potassiumalloy, magnesium, lithium, aluminum, magnesium/copper mixture,magnesium/silver mixture, magnesium/aluminum mixture, magnesium/indiummixture, aluminum/aluminum oxide mixture, or lithium/aluminum mixture,and when these materials are used, a film may be formed by sputtering orvacuum deposition to form an electrode.

The source electrode 35 and the drain electrode 36 may be formed byusing a fluid electrode material such as a solution, a paste, an ink, ora dispersion including the conductive material. The dispersioncontaining metal particles may be, for example, a conductive paste, butany dispersion containing metal particles having a particle diameter ina range of about 0.5 nm to about 50 nm, or, for example, about 1 nm toabout 10 nm may be used. Examples of a material for the metal particlesmay include platinum, gold, silver, nickel, chrome, copper, iron, tin,antimony, lead, tantalum, indium, palladium, tellurium, rhenium,iridium, aluminum, ruthenium, germanium, molybdenum, tungsten, or zinc.

A width and a length of the graphene-based laminate channel layer 34 maybe each in a range of about 20 nm to about 20 μm. However, embodimentsare not limited thereto, and the width and the length of thegraphene-based laminate channel layer 34 may be appropriately controlledaccording to its use.

A material for the insulating layer 33 is not particularly limited aslong as the material has electric insulating property and may be formedinto a thin film. Examples of the material for the insulating layer 33may include a metal oxide (including a silicon oxide), a metal nitride(including a silicon nitride), a polymer, or an organic low molecule,which has an electric resistance rate of about 10 Ωcm or higher at roomtemperature, and, for example, an inorganic oxide film having a highdielectric constant may be used.

Examples of the inorganic oxide may include a silicon oxide, an aluminumoxide, or a hafnium oxide, and a thickness of the inorganic oxideinsulating layer may be in a range of about 100 nm to about 300 nm.Also, the inorganic oxide may include a silicon nitride or an aluminumnitride.

Examples of the insulating layer 33 including an organic compound mayinclude polyimide, polyamide, polyester, polyacrylate, a photo-radicalpolymerization system, a photo-curing resin of a photo-cationicpolymerization system, a copolymer containing an acrylonitrilecomponent, polyvinyl phenol, polyvinyl alcohol, novolak resin, orcyanoethyl flurane.

In addition, wax, polyethylene, polychloroprene, polyethyleneterephthalate, polyoxymethylene, polyvinyl chloride, polyvinylidenefluoride, polymethyl methacrylate, polysulfone, polycarbonate,polyimidecyanoethyl flurane, poly(vinyl phenol) (PVP), poly(methylmethacrylate) (PMMA), polycarbonate (PC), polystyrene (PS), polyolefin,polyacrylamide, poly(acrylic acid), novolac resin, resol resin,polyimide, poly-xylene, or a epoxy resin, as well as a polymer materialsuch as fluranes having a high dielectric constant may be used.

The insulating layer 33 may be a mixture layer including a plurality oforganic or inorganic compound materials as described above, and theinsulating layer 33 may be a stacked laminate. In this case, a materialhaving a high dielectric constant and a material having a waterrepellent property may be mixed or stacked according to the need, andthus a performance of the device may be controlled.

The insulating layer 33 may be formed by using a vacuum depositionmethod, a molecular beam epitaxial growth method, an ion cluster beammethod, a low energy ion beam method, an ion plating method, a CVDmethod, a sputtering method, a dry processing such as an atmosphericpressure plasma method, or a wet processing including a coating processsuch as a spray coating method, a spin coating method, a blade coatingmethod, a dip coating method, a casting method, a roll coating method,or a bar coating method, such as die coating method, or a patterningprocessing such as printing or ink-jet according to the material beingused in forming the insulating layer 33. The wet processing may includea process of coating and drying a dispersion prepared by dispersingparticles of an inorganic oxide in an organic solvent or water by usinga dispersion agent such as a surfactant according to the need, or bycoating and during an oxide precursor, such as an alkoxide solution,i.e., a sol-gel method.

The Si-doped substrate 32 as a back-gate has improved conductivity, andthus a contact resistance between the source electrode 35 and the drainelectrode 36 may decrease due to the Si-doped substrate 32.

The graphene-based laminate may be used in a touch sensor, asemiconductor electrode or device, an electromagnetic wave shielddevice, or a sealing member, as well as in the FET.

Thereinafter, one or more embodiments will be described in detail withreference to the following examples. However, these examples are notintended to limit the scope of embodiments.

EXAMPLE

(Preparation of Graphene-Based Laminate)

Example 1: Preparation of Graphene-Based Laminate

Graphene of a monolayer (thickness of about 0.34 nm) was grown on a 35μm copper foil by using a halogen lamp heater and a rapid thermal CVDdevice.

An acrylate-based adhesive film was attached on the graphenelayer/copper foil laminate. The copper foil was etched by immersing thelaminate in 100 g/L of a sulfuric acid and hydrogen peroxide (H₂SO₄,H₂O₂) solution. Then, the adhesive film/graphene layer laminate waswashed with a predetermined amount of water, attached to a SiO₂substrate, and heated at a temperature in a range of about 100° C. toabout 150° C. Thereafter, the adhesive film was separated from thesubstrate, and thus graphene was transferred.

Then, an LiF layer was deposited on the graphene of a monolayertransferred at a rate of 0.12 Å/s by using a thermal evaporator, andthus a graphene-based laminate was prepared.

Example 2: Preparation of Graphene-Based Laminate

A graphene-based laminate was prepared in the same manner as in Example1, except that a thickness of the LiF layer deposited on the graphenelayer was 5 nm instead of 1 nm.

Example 3: Preparation of Graphene-Based Laminate

A graphene-based laminate was prepared in the same manner as in Example1, except that a thickness of the LiF layer deposited on the graphenelayer was 10 nm instead of 1 nm.

Comparative Example 1: Preparation of Graphene-Based Laminate

A graphene-based laminate was prepared in the same manner as in Example1, except that a thickness of the LiF layer was not deposited on thegraphene layer.

(Preparation of Back-Gated FET)

Example 4: Preparation of Back-Gated FET

The back-gated FET shown in FIG. 4 was prepared.

100 nm of Au patterned by a lift-off process using a photoresist AZ5214was used as a source electrode and a drain electrode. As a channellayer, the graphene-based laminate prepared in Example 1 was used. Alength and width of the channel layer was 20 μm and 19 μm, respectively.The insulating layer was SiO₂ having a thickness of 300 nm.

Examples 5 and 6: Preparation of Back-Gated FET

Back-gated FETs were prepared in the same manner as in Example 4, exceptthat the graphene-based laminates prepared in Examples 2 and 3 wererespectively used as a channel layer instead of the graphene-basedlaminate prepared in Example 1.

Comparative Example 2: Preparation of Back-Gated FET

A back-gated FET was prepared in the same manner as in Example 4, exceptthat the graphene-based laminate prepared in Comparative Example 1 wasused as a channel layer instead of the graphene-based laminate preparedin Example 1.

Analysis Example 1: Light Transmittance Analysis

Graphene of a monolayer (thickness of about 0.34 nm) on the 35 μm copperfoil in Example 1 was transferred onto a glass substrate having athickness of about 800 μm. A graphene-based laminate having the graphenelayer transferred onto the glass substrate was prepared as ComparativeReference Example 1, and a graphene-based laminate prepared bydepositing an LiF layer at a thickness of 5 nm on the graphene layertransferred onto the glass substrate by using the method and the deviceused in Example 1 was prepared as Reference Example 1.

Light of wavelength in a range of about 350 nm to about 800 nm wasirradiated on the graphene-based laminates prepared in Reference Example1 and Comparative Reference Example 1 by using an UV spectrophotometer(U-4100 available from Hitachi) to measure light transmittance of thegraphene-based laminates. The results are shown in FIG. 5.

Referring to FIG. 5, the graphene-based laminate of Reference Example 1(a graphene-based laminate having a LiF layer on a graphene layer) hadonly about 2.3% light transmittance decrease at a wavelength of 550 nm.That is, in terms of light transmittance, the graphene-based laminate ofReference Example 1 (a graphene-based laminate having a LiF layer on agraphene layer) had almost no difference with the graphene-basedlaminate of Comparative Reference Example 1 (a graphene-based laminatethat does not have a LiF layer deposited on a graphene layer).

Analysis Example 2: Raman Spectrum Analysis

Raman light scattering test using a Raman light scattering photometer ofa 514 nm laser (InVia, available from Renishaw) was performed on achannel layer of the graphene-based laminate of the back-gated FET ofeach of Example 5 and Comparative Example 2. The results are shown inFIG. 6.

Referring to FIG. 6, I(2D, 2700 cm⁻¹))/I(G, 1350 cm⁻¹) of the channellayer of the graphene-based laminate of the back-gated FET prepared inComparative Example 2 was about 2.13. I(2D, 2700 cm⁻¹))/I(G, 1350 cm⁻¹)of the channel layer of the graphene-based laminate of the back-gatedFET prepared in Example 5 was about 2.26.

In this regard, it may be known that p-doping was strong and a holecharge concentration decreased in the channel layer of thegraphene-based laminate of the back-gated FET prepared in Example 5.

Evaluation Example 1: Electric Characteristics Evaluation

(1) Electric Characteristics Evaluation 1

Electric characteristics of the back-gated FETs of Examples 4 and 5 andComparative Example 2 were evaluated. A dependent channel current of agate source voltage (V_(GS)) with respect to the back-gated FETs wasmeasured by applying a drain source voltage (V_(DS)=0.3V). The resultsare shown in FIGS. 7A to 7C.

Referring to FIG. 7A, a charge neutral point gate voltage (V_(np)) ofthe back-gated FETs of Examples 4 and 5 moved in a direction of anegative voltage compared to that of the back-gated FET of ComparativeExample 2, but both back-gated FETs maintained a positive voltage. Thus,it may be confirmed that the LiF layer deposited on the graphene layerin the back-gated FETs of Examples 4 and 5 had the graphene layer thatis stably electron doped, and a hole charge concentration was alsocompensated in the graphene layer in the back-gated FETs of Examples 4and 5.

Referring to FIG. 7B, it may be confirmed that field effective mobility(μ_(FE)) of electrons and holes of the back-gated FETs of Examples 4 and5 increased compared to that of the back-gated FET of ComparativeExample 2.

Referring to FIG. 7B, the back-gated FET of Example 5 after 1 year hadalmost the similar curve with that of the back-gated FET of Example 5,except for a small deviation at a high gate voltage.

(2) Electric Characteristics Evaluation 2

Electric characteristics of the LiF layer formed on the graphene layerin the back-gated FETs of Examples 4 to 6 and Comparative Example 2according to a thickness were evaluated. The results are shown in FIGS.8A and 8B.

Referring to FIG. 8A, V_(NP) of the hole charge with respect to athickness of the LiF layer on the graphene layer of the graphene-basedlaminate in each of the back-gated FETs of Examples 4 to 6 had changesof about 10 V, about 35 V, and about 37 V, respectively, compared toV_(NP) of the hole charge of the graphene-based laminate in theback-gated FET of Comparative Example 2.

Referring to FIG. 8A, field effective mobility (μ_(FE)) of hole chargesof the LiF layer on the graphene layer of the graphene-based laminate ineach of the back-gated FETs of Examples 4 to 6 with respect to athickness increased about 150%, about 200%, and about 250%,respectively, compared to a field effective mobility (μ_(FE)) of holecharges of the graphene-based laminate in the back-gated FET ofComparative Example 2.

In this regard, it may be confirmed that the graphene-based laminates inthe back-gated FETs of Examples 4 to 6 had stable electron doping effectand improved charge mobility compared to those of the graphene-basedlaminate in the back-gated FET prepared in Comparative Example 2.

As described above, according to exemplary embodiments, a graphene-basedlaminate including an inorganic layer that includes afluorine-containing lithium compound and is formed on a graphene layermay have electron doping stability and improved electron mobility. Also,a method of preparing the graphene-based laminate may improve electronmobility and may be economical.

It should be understood that embodiments described herein should beconsidered in a descriptive sense only and not for purposes oflimitation. Descriptions of features or aspects within each embodimentshould typically be considered as available for other similar featuresor aspects in other embodiments.

While exe embodiments have been described with reference to thedrawings, it will be understood by those of ordinary skill in the artthat various changes in form and details may be made therein withoutdeparting from the spirit and scope of the inventive concept as definedby the following claims.

What is claimed is:
 1. A graphene-based laminate comprising: asubstrate; a graphene layer consisting of graphene formed directly on atleast one surface of the substrate; and an inorganic layer formeddirectly on the graphene layer and comprising a fluorine-containinglithium compound, wherein the graphene layer is provided between thesubstrate and the inorganic layer, and the substrate and the inorganiclayer are not in contact with each other, and wherein an averagethickness of the inorganic layer is in a range of about 0.1 nm to about10 nm.
 2. The graphene-based laminate of claim 1, wherein an inorganicmaterial included in the inorganic layer is represented by a followingformula:Li_(x)F_(y) wherein, x satisfies 1≤x≤10, and y satisfies 1≤y≤10.
 3. Thegraphene-based laminate of claim 1, wherein the inorganic materialcomprises at least one compound selected from LiF, LiF₂, LiF₃, Li₂F, andLi₃F₃.
 4. The graphene-based laminate of claim 1, wherein an averagethickness of the inorganic layer is in a range of about 0.1 nm to about5 nm.
 5. The graphene-based laminate of claim 1, wherein the graphenelayer comprises one layer or a plurality of layers less than or equal toten layers.
 6. The graphene-based laminate of claim 1, wherein thegraphene layer has defects on a surface thereof.
 7. The graphene-basedlaminate of claim 1, wherein the substrate comprises at least onematerial selected from a polymer-based material, a silica-basedmaterial, and a metal oxide-based material.
 8. A transistor comprising:a gate layer; a substrate and an insulating layer formed above the gatelayer; a source electrode and a drain electrode formed above theinsulating layer; and the graphene-based laminate of claim 1 contactingthe source electrode and the drain electrode and disposed therebetween.9. The graphene-based laminate of claim 1, wherein the graphene-basedlaminate consists of the substrate, the graphene layer and the inorganiclayer.
 10. An organic light emitting device comprising: a firstelectrode comprising the graphene-based laminate of claim 1; a holeinjection layer formed above the first electrode; a hole transport layerformed above the hole injection layer; an emission layer formed abovethe hole transport layer; an electron transport layer formed above theemission layer; an electron injection layer formed above the electrontransport layer; and a second electrode.
 11. The organic light emittingdevice of claim 10, wherein the first electrode may be formed of atleast one of indium tin oxide (ITO), indium zinc oxide (IZO), tin oxide(SnO₂), zinc oxide (ZnO), aluminum (Al), silver (Ag), magnesium (Mg).12. A method of preparing a graphene-based laminate, the methodcomprising transferring a graphene layer consisting of graphene directlyonto a target substrate to dispose the graphene layer directly on atleast one surface of the target substrate; and depositing an inorganiclayer including a fluorine-containing lithium compound directly on thedisposed graphene layer, wherein the graphene layer is provided betweenthe substrate and the inorganic layer, and the substrate and theinorganic layer are not in contact with each other, and wherein anaverage thickness of the inorganic layer is in a range of about 0.1 nmto about 10 nm.
 13. The method of claim 12, wherein the inorganicmaterial included in the inorganic layer is represented by Formula 1:Li_(x)F_(y) wherein, x satisfies 1≤x≤10, and y satisfies 1≤y≤10.
 14. Themethod of claim 12, wherein the graphene layer comprises one layer or aplurality of layers less than or equal to ten layers.
 15. The method ofclaim 12, wherein the transferring the graphene layer to the targetsubstrate further comprises etching the target substrate.
 16. The methodof claim 12, wherein the target substrate comprises a material selectedfrom a polymer-based material, a silica-based material, and a metaloxide-based material.
 17. The method of claim 12, wherein the depositingthe inorganic layer is performed by thermal chemical vapor deposition.18. The method of claim 12, wherein the graphene-based laminate consistsof the substrate, the graphene layer and the inorganic layer.
 19. Themethod of claim 12, wherein the graphene layer is grown on thesubstrate, on which graphene and graphitized catalyst layer are formed.20. The method of claim 19, wherein the graphene and the graphitizedcatalyst layer comprises a catalyst selected from Cu, Ni, or an alloythereof.